While microbially mediated coupling process of nitrate reduction and Fe(II) oxidation (NRFO) plays important role in widespread nitrogen and iron biogeochemical cycles in the natural environments, the underlying mechanism of NRFO is still not clearly understood. Here, N and O isotope fractionation during microbial nitrate Pseudogulbenkiania reduction by sp. strain 2002 with or without Fe(II) were investigated. The nitrate reduction rate decreased substantially in the presence of Fe(II), and cells became encrusted with Fe(III) minerals. ε However, the N isotope enrichment factors ( ) with or without Fe(II) were identical within uncertainty (24.1 ± 2.4‰ and 25.1 ± 2.4‰), implying that Fe(II) oxidation had little influence on the extent of N isotope fractionation and that cell encrustation was unlikely to cause additional mass transfer limitation. Isotopic 18 15 18 15 ε ε composition ratios of O to N ( : ) were 0.73 ± 0.13 with and 0.50 ± 0.08 without Fe(II), close to reported values for nitrate reduction by periplasmic nitrate reductases, implying that enzymatic nitrate reduction mainly occurs in strain 2002's periplasmic space. A kinetic model based on elementary reactions was established, and rate constants of enzymatic nitrate reducing reactions were obtained in a living cell system. Combining dual N- O isotope fractionation analysis with kinetic modeling is a promising approach for interpreting diverse enzymatic pathways during NRFO processes.

Chen, J., Jia, W., Xiao, Z., Peng, P.a., 2020. Catalytic hydropyrolysis of asphaltenes in marine oil from the Tarim Basin, NWChina: Implications to complicated oil charging histories in an old composite basin. Marine and Petroleum Geology 114, 104232.

http://www.sciencedirect.com/science/article/pii/S0264817220300155 Oil asphaltenes have been used to characterize the source(s) and timing of expulsion of early charged oils. However, the application on asphaltene in a complex petroleum basin have been limited. Marine oils from the Tarim Basin, NWChina, were selected to release asphaltene-bound molecules by the catalytic hydropyrolysis technique (Hypy). The analyzed samples were 10 heavy oils from two major oil-production regions (the Tabei and Tazhong uplifts) in the basin. The asphaltenes may be mixed products from multiple hydrocarbon charging stages, if we consider the main oil filling events and the regional geothermal histories of corresponding reservoirs. However, the similar molecular and isotopic characteristics of the hydropyrolyzates indicate contributions from one major source rock (possibly lower Cambrian mudstone) during relatively early periods, based on the presently known source characteristics. The preservation of asphaltenes probably reflects a low reservoir temperature after charging. The asphaltenes were derived from marine algae deposited in a strongly reducing environment, given the biomarker data (e.g., relatively abundant aryl isoprenoids and low Pr/Ph) and carbon isotopic data (-35.5‰ to -34.4‰). Asphaltenes were expelled around the oil generation p eak. Moreover, molecular ratios indicative of maturity (e.g., tricyclic terpanes/hopanes), derived by Hypy of asphaltenes, suggest that the asphaltenes of the Tazhong Uplift are generally more mature than those of the Tabei Uplift. Moreover, this is mainly related to different maturities when the oil was expelled. The free hydrocarbons in the Tazhong Uplift show greater molecular and isotopic variations than those in the Tabei Uplift. This might be attributed to more complex accumulation processes in the former. Late oils with a range of maturities, mixing proportions with early biodegraded oils, and degrees of alteration by thermochemical sulfate reduction could all have played a role in generating this variability. The results indicate that the hydrocarbons released from oil asphaltenes by Hypy can provide insights into multiple charging processes in an old composite petroleum basin.

Chen, L., Jin, M., Wang, X., Wang, H., Li, N., 2020. The effects of diagenetic processes and fluid migration on rare earth element and organic matter distribution in seep-related sediments: A case study from the South China Sea. Journal of Asian Earth Sciences 191, 104233.

http://www.sciencedirect.com/science/article/pii/S1367912020300080 Methane seepage is an important factor governing microbial activity in marine sediments, although its impact on the distribution of rare-earth elements (REEs) and organic matter in sediments is unclear. Here, we report 13 13 isotope signatures of organic (δ C ) and inorganic (δ C ) carbon as well as total REEs contents of core TOC TIC sediments collected from a well-characterized seep area on the northern South China Sea. Previous studies have identified sediments corresponding to three methane-release events (MREs) in the studied core: MREI at 4.0 - 5.5 m, MREII at 7.4 - 8.2 m, and MREIII at 10.0 - 11.5 mdepth intervals. Increased methane flux and reducing